This invention relates to a pattern forming method and, in particular, relates to a pattern forming method that processes a coating layer over a substrate into a predetermined pattern by partly removing the coating layer and then forms a recess in an underlying layer below the coating layer at its portion corresponding to at least a portion of a region where the coating layer was removed.
This invention also relates to a method of manufacturing a phase shift mask for use in transferring a fine pattern of an LSI or the like by the use of a projection exposure apparatus and, in particular, relates to a method of repairing a residue defect generated at an underlying layer below a light-shielding layer in the manufacturing process.
Following higher integration and circuit pattern miniaturization in large-scale integrated circuits (LSIs), phase shift masks have been proposed and put to practical use as a super-resolution technique in the photolithography.
There have been proposed various types of phase shift masks, such as Levenson type, edge emphasizing type, auxiliary pattern type, chromeless type, and halftone type. For example, the Levenson type phase shift mask has a light-shielding pattern formed by a metal film such as a chromium film, or the like on a transparent substrate. The Levenson type phase shift mask is configured such that, in the case where light-shielding portions and light-transmitting portions are alternately arranged like a line-and-space pattern, the phases of transmitted lights through the light-transmitting portions adjacent to each other via each light-shielding portion are shifted by 180 degrees. Because of the shift in phase between the transmitted lights through the light-transmitting portions, a reduction in resolution due to interference between diffracted lights can be prevented to thereby achieve an improvement in resolution of the line-and-space pattern.
In such a phase shift mask, an optical path length difference of [λ(2m−1)/2] (m is a natural number) is generated between transmitted lights, each having a wavelength λ, through the light-transmitting portions adjacent to each other via the light-shielding portion, thereby causing the phase difference of 180 degrees between the transmitted lights. In order to generate such an optical path length difference, a difference d between the thicknesses of the transparent substrate at the light-transmitting portions adjacent to each other via the light-shielding portion should satisfy [d=λ(2m−1)/2n] where n represents a refractive index of the transparent substrate.
In order to generate the difference between the thicknesses of the transparent substrate at the adjacent light-transmitting portions in the phase shift mask, a transparent thin film is coated on the transparent substrate at one of the light-transmitting portions to thereby increase the thickness or the transparent substrate is etched at one of the light-transmitting portions to thereby reduce the thickness. That is, in the shifter coated type (convex type) phase shift mask, the transparent substrate is covered with the transparent thin film (shifter) having the thickness d (=λ(2m−1)/2n) at the phase shift portion.
On the other hand, in the etching type phase shift mask in which the transparent substrate is etched, the transparent substrate is etched by the depth d (=λ(2m−1)/2n) at the phase shift portion. The light-transmitting portion not coated with the transparent thin film or etched serves as a non-phase-shift portion. Note that in the case where the adjacent light-transmitting portions have a shallow etched portion and a deep etched portion, respectively, the shallow etched portion serves as a non-phase-shift portion.
Further, as a phase shift mask for forming an isolated pattern such as contact holes, the auxiliary pattern type phase shift mask has been proposed as described in Japanese Patent (JP-B) No. 2710967 (Patent Document 1).
FIGS. 1A to 1C show the structures of auxiliary pattern type phase shift masks, wherein FIG. 1A is a plan view of the auxiliary pattern type phase shift mask (the plan view is the same for both masks) and FIGS. 1B and 1C respectively show sections, each taken along a chain line A in FIG. 1A, in terms of two examples.
In FIGS. 1A to 1C, each auxiliary pattern type phase shift mask comprises a transparent substrate 101 and a light-shielding layer 102 formed thereon, wherein the light-shielding layer 102 is formed with a main opening portion 103 and a plurality of auxiliary opening portions 104 located at peripheral portions of the main opening portion 103. It is configured such that light having passed through the main opening portion 103 and light having passed through each auxiliary opening portion 104 have a phase difference of approximately 180 degrees. For this purpose, in the example shown in FIG. 1B, the transparent substrate 101 has an etched portion 105 etched to a predetermined depth in a region corresponding to the main opening portion 103. On the other hand, in the example shown in FIG. 1C, the transparent substrate 101 has etched portions 105, each etched to a predetermined depth, in regions corresponding to the auxiliary opening portions 104, respectively. The auxiliary opening portions 104 are formed at predetermined positions and each have a fine line width so that the light having passed through each auxiliary opening portion 104 does not resolve a resist on a substrate to which a pattern is transferred.
FIGS. 2A to 2F are process diagrams showing a conventional phase shift mask manufacturing method.
For manufacturing an auxiliary pattern type phase shift mask like that shown in FIG. 1C, a light-shielding layer 102 and a first resist film 106 are first formed on a transparent substrate 101 in the order named as shown in FIG. 2A. Then, as shown in FIG. 2B, the first resist film 106 is written with a pattern corresponding to a main opening portion 103 and a plurality of auxiliary opening portions 104 by the use of, for example, an electron-beam writing apparatus and then developed, thereby forming a first resist pattern 107. Then, the light-shielding layer 102 is etched using the first resist pattern 107 as a mask, thereby forming a light-shielding layer pattern 108 having the main opening portion 103 and the auxiliary opening portions 104. Thereafter, as shown in FIG. 2C, the remaining first resist pattern 107 is stripped.
Then, as shown in FIG. 2D, a second resist film 109 is formed on the light-shielding layer pattern 108. Subsequently, as shown in FIG. 2E, the second resist film 109 is written with a pattern corresponding to the auxiliary opening portions 104 by the use of, for example, the electron-beam writing apparatus and then developed, thereby forming a second resist pattern 110. Then, the transparent substrate 101 is etched using the second resist pattern 110 as a mask, thereby forming etched portions 105. Thereafter, as shown in FIG. 2F, the remaining second resist pattern 110 is stripped, thereby completing an auxiliary pattern type phase shift mask.
In the manufacturing method shown in FIGS. 2A to 2F, the transparent substrate 101 is etched in regions corresponding to the auxiliary opening portions 104. However, the same manufacturing method is also applied to the case where the transparent substrate 101 is etched in a region corresponding to the main opening portion 103. That is, in FIG. 2E, the second resist film 109 is written with a pattern corresponding to the main opening portion 103 and then developed, thereby forming a second resist pattern. Subsequently, the transparent substrate 101 is etched using this second resist pattern as a mask, thereby forming an etched portion 105 like that shown in FIG. 1B.
Further, as a phase shift mask for forming an isolated pattern such as contact holes, there is a halftone type phase shift mask.
FIGS. 3A to 3G are process diagrams showing a conventional halftone type phase shift mask manufacturing method.
For manufacturing a halftone type phase shift mask, a light-semitransmitting layer 111, a light-shielding layer 102, and a first resist film 106 are first formed on a transparent substrate 101 in the order named as shown in FIG. 3A. Then, as shown in FIG. 3B, the first resist film 106 is written with a hole opening pattern by the use of, for example, an electron-beam writing apparatus and then developed, thereby forming a first resist pattern 107. Then, the light-shielding layer 102 is etched using the first resist pattern 107 as a mask, thereby forming a light-shielding layer pattern 108. Thereafter, as shown in FIG. 3C, the remaining first resist pattern 107 is stripped.
Then, as shown in FIG. 3D, the light-semitransmitting layer 111 is etched using the light-shielding layer pattern 108 as a mask, thereby forming a light-semitransmitting layer pattern 112. Further, as shown in FIG. 3E, a second resist film 109 is formed on the light-shielding layer pattern 108. Then, as shown in FIG. 3F, the second resist film 109 is written with a pattern corresponding to a main opening portion 113 by the use of, for example, the electron-beam writing apparatus and then developed, thereby forming a second resist pattern 110. Then, the light-shielding layer 102 is etched using the second resist pattern 110 as a mask, thereby forming a light-shielding layer pattern 114. Thereafter, as shown in FIG. 3G, the remaining second resist pattern 110 is stripped, thereby completing a halftone type phase shift mask.
Note that, in this case, the light-semitransmitting layer 111 and the light-shielding layer 102 are respectively made of materials each having resistance to the etching of the other material.
In either of the foregoing phase shift mask manufacturing methods, the etching is performed a plurality of times for manufacturing a single phase shift mask. Therefore, as compared with the manufacture of a normal photomask that requires only one-time etching of a light-shielding layer, the phase shift mask manufacturing method is complicated in fabrication process and takes much time, resulting in higher defect generation probability.
In the manufacture of a phase shift mask as described above, a residue defect may be generated due to the incorporation of dust or the like at the time of etching. The residue defect is a defect in which a portion that should be etched is not etched. For repairing such a residue defect, there is applied a method of etching a residue-defect portion by the use of laser light or FIB (Focused Ion Beam), a method of shaving off a residue-defect portion by the use of a superfine needle, or the like.
With respect to a defect generated in the second etching of the light-shielding layer 102 in the halftone type phase shift mask, the global repair is enabled as described in Japanese Patent (JP-B) No. 3650055 (Patent Document 2).
In the meantime, with respect to a defect generated in the manufacture of a phase shift mask as described above, chances of repairing thereof depend on its generation process or its type. That is, in either of the foregoing manufacturing methods, for example, if a defect generated in the first etching of the light-shielding layer 102 is huge or very small or if it is generated at a plurality of portions or has a complicated shape, it is difficult to ensure accuracy of repairing thereof and the time required for the reparing is quite long according to the foregoing various repairing methods. In view of this, it should be judged that it is practically impossible to repair the defect generated in the first etching of the light-shielding layer 102.
On the other hand, it is possible to repair a defect generated in the etching of the transparent substrate 101 or the light-semitransmitting layer 111 after the first etching of the light-shielding layer 102. However, there is also a problem in repairing accuracy and repairing time according to the foregoing various repairing methods and, therefore, there is required a manufacturing method that enables accurate repairing more easily.
Incidentally, the repairing method described in Patent Document 2 is intended for the defect generated in the second etching of the light-shielding layer 102 in the halftone type phase shift mask and cannot deal with the defect generated in the etching of the transparent substrate 101 or the defect generated in the etching of the light-semitransmitting layer 111.